Means for neutralizing sound distortion



Feb. 1, 1938.

W. WILSON MEANS FOR NEUTRALIZING SOUND DISTORTION 3 Sheets-Sheet 1Original Filed April 24, 1923 AMPLIFIER LOUD SPEAKER LlGHT AMPLIFIERLIGH CONTBI. [ONTRUL AMPLIFIER EINPuf AMPLIFIER wzzzvroza.

gram. I

fink/PW V A TTORNEYS.

w. WILSON 2,107,135

MEANS FOR NEUTRALIZING SOUND DIS'IORTION Original Filed April 24, 1929 5SheetsSheet 2 Feb. I, 1938.

.37 39 I; IN PUT J AMPLIQFIER AMPUFIER k 2a B A -1 fi E; IN PUTANPLIFIEL 1 "1' 7 I g 7) I I E 'NPUT AMPLIFIEk AMPLIFIER AMPLIFIER L0EINPUT AMPUFIER I v g 1 VENTOR.

' BY I 3 and/MUM ATTORNEYS.

Feb. 1, 1938. w. WILSON 2,107,135 MEANS FOR NEUTRALIZING SOUNDDISTORTION I Original Filed April '24, 1929 3 Sheets-Sheet 5 PatentedFeb. 1, 1938 UNITED STATES PATENT OFFEQE Wesley Wilson, Chicago, Iii.

Application April 24, 1929, Serial No. 357,861 Renewed August 13, 1937 9Claims trical circuits and energy transformers of sound 7 recording andreproducing apparatus in which the permanent record is made onphotographic film. These film records can be so made as to tend tocounteract distortion arising within the recording and reproducingapparatus. This is not only an advantage in reducing distortion whichcan not be overcome by the methods of construction in vogue but alsowhere a saving or simplification in the construction of the apparatuswould be effected if it were not necessary to reproduce the record withperfect fidelity.

This invention is also adaptable to radio broadcasting and television,in which case the electrical impulses or waves could be distortedreversely at the broadcasting station to the distortion arising withinthe reproducing apparatus.

Another possible method of utilizing this invention is in secretcommunication such as telephony and the transmission of pictures byradio. In this method it would be necessary to artificially causedistortion in the receiving apparatus to such an extent that the reversedisvtortion necessary in the sending apparatus (to counteract thedistortion in the receiving apparatus) would be so great that the signalwould be unintelligible if reproduced on apparatus not having the properdistortion.

Among the objects of my invention are to reduce the degree of distortionarising within translating devices by distorting the electrical waves(which operate or are operated by said devices) in the reverse directionto the distortion produced in the waves by the translating device; totend to neutralize the distortion arising within sound or picturerecording and reproducing apparatus by deliberately distorting therecords (which are made and reproduced by this apparatus) in the reversedirection to the distortion arising within said apparatus.

A further object of my invention is to provide a method of correctingthe effect of distorting characteristics in part of a sound controllingapparatus, comprising the introduction into the sound controllingapparatus of additional apparatus having distorting characteristicssimilar to the distorting characteristics of said part in such mannerthat the distortion caused by the introduced apparatus counteracts theeffect of the distortion produced by said part.

It will be understood that the following description relates more tothis example of the practice of the invention and that the inventionwill be defined in the appended claims.

Further objects will appear from the description and claims.

In the drawings, in which several embodiments of my invention are shownFigure 1 is a diagrammatic view showing apparatus for making a soundrecord on photographic film and counteracting the efiect of thedistorting characteristics of the reproducing and recording apparatus;

Fig. 2 is a face View of a portion of the photographic film showingdiagrammatically the direct sound record and the counteracting soundrecord;

Fig. 3 is a view similar to Fig. 2 but showing 4 diagrammatically adifferent type of sound record;

Fig. 4 is a view showing diagrammatically the manner in which the twosound records of Fig. 2 may be combined in a single record at the sideof the film;

Fig. 5 is a face view showing diagrammatically how the two sound recordsof Fig. 3 may be combined in a single record, at the side of the film;

Fig. 6 is a diagrammatic view showing apparatus for reproducing thesound from photographic film similar to that shown in Figs. 2 and 3;

Fig. '7 is a diagrammatic view showing apparatus for counteracting atthe broadcasting station the efiect of distorting characteristics in theaudiofrequency amplifier system of a radio receiving set;

Fig. 8 shows apparatus for counteracting the eifect of distortingcharacteristics in amplifying and reproducing apparatus in which thecounteraction or reverse distortion is effected electrically;

Fig. 9 shows apparatus for counteracting the effect of distortionarising within a loud speaker in which the reverse distortion iseffected by energy dissipation; and

Fig. 10 is a chart showing curves plotted from the table at the end ofthe specification.

The basic idea underlying the various form of my invention shown is amethod of correcting the effect of distortion arising within translatingdevices (such as electrical sound reproducers, transformers,microphones, light control valves, etc.) by utilizing additionalapparatus having approximately the same distorting characteristics asthe device producing the objectionable distortion, in such a manner thatthe distortion caused by he introduced apparatus will have acounteracting eifect with respect to the objectionable distortion. Forexample, if a film record is made ofa violin solo by recording apparatuswhich produces distortion in the record in varying degrees and atcertain definite frequencies itis obvious that this distortion will bereproduced in the reproducing apparatus. Now, if there is distortion.also in the reproducing apparatus it is also obvious that thisdistortion will also show up in the reproduced violin solo. That is,there will be a variation in the equivalent value of the correspondingnotes or frequencies in the original violin solo and the solo that isreproduced from the film record. If this same recording apparatus isused to make a record of the sound that is reproduced by passing theoriginal record through the reproducing apparatus, it is obvious that inthis second record, which we will call the secondary record, the equivalent value of the notes will vary from the corresponding notes in theoriginal record at all points where there was distortion in thereproducing apparatus or in the recording apparatus as it was making thesecondary record,

If in either the reproducing or recording apparatus the efiiciency isvery low when handling notes of one particular frequencyv it will resultin the recording of this note on the secondary record at an equivalentvalue below that of the original record. Now, if the efiiciency at thisfrequency was lowered in the recording apparatus it would mean that theequivalent value of the note on i the original record would be loweredby this distortion and would again be lowered on the secondary record.If all of the distortion were in the reproducing apparatus at thisfrequency it would me'anthat on the original record this note would nothave its equivalent value lowered but would be lowered on the secondaryrecord.

Therefore, in either case the equivalent difference between the tworecords would depend upon the distortion in the reproducing apparatus orin the recording apparatus when recording the secondary record. Oranother way of saying it is that the equivalent differences betweencorre-, sponding notes on the original and secondary records are similarto the equivalent differences between the notes of the original violinsolo and the corresponding notes of the reproduced solo. Now, a way toneutralize this effect of distortion arising within the recording andreproducing apparatus is to distort the film record in the reversedirection to the distortion arising within said apparatus' That is, ifthe equivalent value of a particular note or frequency is lowered bydistortion in either the recording or reproducing apparatus the filmrecord should have this note recorded at a higher equivalent value inorder to neutralize it. As the distortion recorded on the original andsecondary records is in the same direction (but in different degrees) asthe distortion arising within said apparatus, it follows that thedesired film record (which will be called the neutralized record) shouldbe distorted reversely to the distortion in the original and'secondaryrecord.

Now, as the equivalent value of notes on the secondary record have beenlowered below the equivalent value of corresponding notes on theoriginal record to the extent resulting from distortion caused bypassing once through the reproducing and recording apparatus it followsthat notes or frequencies which have been distorted the most will havethe greatest difference between their equivalent value on the primaryand secondary records. If the notes or frequencies recorded on thesecondary record are made to partially neutralize the correspondingnotes on the primary record and the resultant effect recorded on a thirdfilm it will be found that this third filmwill be distorted in theproper direction to at least partially neutralize the effect ofdistortion arising within the said apparatus. By varying the degrees ofneutralization between the original (primary) and secondary record whenmaking the neutralizing record, it is possible to obtain the mostadvantageous degree of neutralizing distortion. Bearing in mind that theequivalent value of corresponding notes on the primary (original) andsecondary records are identical when there is no distortion in theapparatus it becomes apparent that the notes that will be neutralizedthe most will be the ones that were weakened the least by distortionwithin the said apparatus. In actual practice this method is quiteimpractical and is of value only as a means of explaining the theory ofthe invention: Instead the electrical waves from the pick-up apparatusreceiving the original sound waves are divided and made to flow throughtwo parallel channels. One is provided with additional apparatus forproducing distortion similar to the objectionable distortion andcontrols alight valve. The other channel also controls a light valve buthas no additional apparatus for deliberately producing distortion. tothe system shown in Fig. l of the drawings.)

The light fluctuations from these valves are recorded on the same film,either side by side (as shown in Figs. 2 and 3) so as to make two sepa-.

rate records (which would correspond to the original and secondary filmrecords and which could be made to partially neutralize each other inthe reproducing apparatus as. in Fig.6)v or the two records could besuperimposed (as shown.

in Figs. 4 and 5) if care were. taken to insure that the recorded lightfrom one valve neutralized the sound reproducing quality of the recordedlight from the other valve, to such an extent as to produce the properdegree of reverse distortion.

The electrical waves from the two channels can be made to partiallyneutralize each other direct (as shown in Fig. 8) if a means is providedfor maintaining the time lags in the channels identical. Such anarrangement would'be adaptable to public address systems, radiotelephony; the making of wax records for phonograph reproduction, etc.

Referring to the drawings in detail, and first to the apparatus shown inFigs. 1 to 3, inclusive, this comprises in general, apparatus'forproducing sound records on photographic films, which films, after havingthe sound record made thereon, may thereafter be used in the soundreproducing apparatus in Fig. 6. The apparatus shown in Fig. 1 comprisessound pickup which may be of any usual or suitable type, including inputmeans I and, amplifying means 2, a light control apparatus 3 controlledby the microphone, for producing a sound-record on the film 4corresponding to the received sound, and a corrective circuit forcounteracting the effect of the distorting characteristics of theapparatus shown in Fig. 6 and also input I and amplifier 2. It is wellknown that reproducing apparatus, such 'as shown in Fig. 6, almostnecessarily possesses distorting of the sound record more than it willdistort (This is similar other portions; that is to say, certainfrequencies may be reproduced well and with little loss of volume, whileother frequencies may be reproduced poorly; that is, with considerableloss of volume. It is with a view to equalizing this distortion or lossof volume that the present apparatus is designed. In order to effectthis equalizing or counteracting effect, certain apparatus is introducedinto the recording apparatus of Fig. 1, including an amplifier andspeaker 6 (which should be identical with or similar to the arm plifierl and speaker 8 of the apparatus of Fig. 6), receiving means 9 for soundtransmitted by the speaker 6, which should have characteristics similarto input i, amplifying means II! (which should be similar to 2) for thereceiver 9, and light control apparatus H for causing a sound record tobe made on photographic film 4 which can be made to correct the effectof distortion due to the distorting characteristics of the reproducingapparatus of Fig. 6, and also input I and amplifier 2 of Fig. 1.

In order to take care of the time lag caused by the fact that thereceiver 9 is necessarily placed an appreciable distance from thespeaker 6, the recording point A2 of the light control apparatus I! ofthe corrective circuit may be ad vanced a slight distance in thedirection of film movement from the recording point I? of the lightcontrol apparatus 3 of the direct circuit, the distance A having such arelation to the distance B that it will counteract the time lag due tothe spacing between the receiver 9 and the speaker 6.

Bearing in mind that the amplifier 5 and speaker B of the correctivecircuit have distorting characteristics substantially the same as thedistorting characteristics of the amplifier l and speaker 8 of thereproducing apparatus of Fig. 6 and that the receiver 9 and amplifier IDof Fig. 1 are similar to the input means I and amplifier 2 of Fig. 1,and also that the record made from light control 3 will correspond tothe direct (primary) record, while the record made from light control IIwill correspond to the secondary record (which will be recorded inopposite phase). Recording in opposite phase may be accomplished byreversing the electrical connections, as shown clearly in Figs. 7, 8,and 9. Fig. 1 has a reversed connection between receiver 9 and amplifierID in that the upper conductor becomes the lower conductor on making thebend. It will be seen that there can be effected a partialneutralization of the direct record by the secondary record by properlyadjusting light sources 25 and 26 of Fig. 6 which will produce thecounteracting (reverse distorting) efiect. Thus those parts of therecord which would otherwise be reproduced with too great a volume willhave this volume automatically cut down by the corrective circuit to aconsiderable extent, while those parts of the record which arerelatively poorly reproduced in the apparatus of Fig. 6 will have theirvolume cut down comparatively little, by the corrective circuit ofFig. 1. By recording these two records on the same film no troubleshould be encountered in permanently maintaining them in the properphase relation. If recorded on separate recording medium this would bepractically impossible to do. If the primary and the secondary recordsare made side-by-side, either as a variable density record as shown inFig. 2, or as the variable width method as shown in Fig. 3, it will notbe necessary to accurately control the relative intensities at which thetwo records are recorded. All that is necessary is that the two recordsbe 180 out of phase.

Fig. 2 shows one type of film record (known as the variable densitytype) which might be made by the apparatus shown in Fig. 1. The directprimary undistorted record 14 is alongside the secondary distortedrecord 55 with the corresponding portions in opposite phase (that is,one record passing the most light where the other record passes theleast light). By using the entire Width of the film for these records,the efi'ect of film noises (caused by the granular structure of thephotographic emulsion) is reduced.

This film record is adaptable for use on reproducing apparatus of Fig.6. With such an arrangement the degree of reverse distortion isadjustable, it being necessary only to change the relative amount oflight passing through the two records to vary the degree of partialneutralization. This is due to the fact that the sound reproduced inspeaker 8 is dependent only upon the fluctuating component of the lightstriking the photoelectric cell and not upon the total quantity, thenonfiuctuating component of light being of zero frequency.

Fig. 3 shows a different type of record known as the variable width typein which the amount of iight transmitted through the film is propor-.tional to the width of the transparent portion ll of the record.Otherwise it is the same as Fig. 2.

Fig. 4 shows a film in which the direct and secondary records I land I5of Fig. 2 have been superimposed or combined intoa narrow record 18 atthe side of the film, leaving the rest of the film to be used for motionpicture reproduction. With such an arrangement the degree of reversedistortion is fixed at the time the film is made and, therefore, must beaccurately controlled in the making.

Fig. 5 shows a film in which the direct and secondary sound records ofFig. 3 have been combined into a single narrow sound record l9 at theside of the film leaving the rest of the film for the reproduction ofmotion pictures and is similar in characteristics to that of Fig. 4.

Fig. 6 shows the use of the sound record film t which is similar to thefilm shown in Fig. 2 or 3 produced by the apparatus of Fig. l in a soundreproducing apparatus having light apertures 20 and 2! for the directand secondary sound record, feed apparatus 22 for the film, and a lens23 for bringing the light which passes through the sound records intoproper relation to a photoelectric cell controlling the amplifier andspeaker 3. Light from sources 25 and 26 is directed against apertures25! and 2i, respectively. Thereby having a separate light source for thedirect and secondary records and thereby making it possible to manuallyvary the degree of reverse distortion continuously during thereproduction of a record so as to obtain the best results at all times.

Fig. '7 shows a method of reversely distorting a radio broadcastingsignal so as to effectively neutralize the distortion in all receivingsets using a particular type of amplifier, amplifier 21 to be as nearlyperfect as possible and to correspond to the direct circuit whileamplifier 28 to be the same as that used in the said receiving sets, andto correspond to the secondary or corrective circuit. The output fromamplifier 28 is made to partially neutralize that of amplifier 21 andthereby obtain this reverse distorting efiect electrically. Amplifiers2i and 28 may be of the push pull type so as to eliminate harmonics,etc.

Figi 8 shows how it would be possible to ac complish this reversedistortion for neutralizing the distorting characteristics of a loudspeaker without first permanently recording the sound.

The fundamental difference between this circuit and the previous ones isin the way of avoiding the time lag encountered by the air gap A betweenspeaker B and microphone C. This is accomplished by having two pick-upmicrophones D and Er located at different distances from the source ofsound. Microphone D picks up the sound for the circuit having theartificial distortion and which would correspond to the circuit usedforthe making of the secondary record of Fig. l. Microphone E (which islocated at a greater distance from the sound source than D) operates thecircuit having no artificial distortion and which would correspond tothat part of Fig. 1 which records the direct record. 7

By properly adjusting the distance of microphone E from the sound sourcein relation to microphone Dv it will readily be seen that the time lagbetween speaker B and microphone C will be balanced out. When the soundwhich is to be picked up comes from many different points it isnecessary that the mouth pieces of the microphones D and Ev be locatedside-by-side or even converge into one in order to obtain the propertime lag between the two microphones. This is accomplisheddiagrammatically in the figure in the form of a tube F which has theproper acoustical properties and extends from microphone E to a pointadjacent to the mouth piece of microphone D.

Fig. 9 shows a still different way of carrying V out the objects of thisinvention and consists of two parallel circuits, energized by the samesource, which may be similar to each other with the exception that inone of the circuits a loud speaker is inserted (having characteristicssimilar to that of the speaker which is to do the final reproduction) insuch a way as to dissipate the electrical energy impressed upon it inthe form of sound energy. Now the frequencies at which the speakeroperates most efiiciently at will will also be the ones that have thegreatest amount of energy dissipated. The result will be that thedistortion produced in this circuit by this energy dissipation will bein the desirable direction.

However, it will not be suiiicient to produce the most advantageousresults and, therefore, it will be necessary to partially neutralize bythe relatively undistorted energy of the other circuit in order toincrease this reverse distortion sufficiently.

Referring to Fig. 10, this is a diagram exhibiting the relativedistortion correction that may be effected by the practice of myinvention, as, for example, when using apparatus similar to that of Fig.1.- The vertical lines denoted by the letters A to J, represent variousfrequencies handled by the apparatus and which correspond to the soundfrequencies which are to be reproduced. The horizontal lines representthe relative energy levels at which the said various frequencies arereproduced, the scale of which is logarithmically shown to the left asthe relative energy levels shown in percent, while to the right areshown the corresponding values in TU (transmission units, defined by theequation TU=1O log. [P11 2] when [P1P2l is the power ratio.) The linearrelation shown by curve Q represents the relative reduction in volume ofthe various important frequencies of a recording and reproducingapparatus when employing no reing apparatus.

verse distortion as practiced by this invention. The values for thiscurve are arbitrary and have conveniently been assumed to vary from 100%perfect reproduction to 10% perfect reproduction. t should be understoodthat any point on this curve may represent a large number of diiferentfrequencies that may happen to be reproduced with the same degree ofefiiciency.

The line P of Fig. 10 is assumed to represent the desired energy levelat which all frequencies should be reproduced in order to give theproper volume of undistorted sound under a given condition.

The curve R of Fig. 10 represents the amount of distortion correctionthat may be effected by the practice of this invention when usingapparatus similar in its distorting characteristics to the apparatusused to obtain curve Q.

At the end of the Specification is a table showing how the arbitraryvalues for curve R have been obtained. In this table' Column 1 denotesthe various frequencies which are so distorted in the recording andreproducing apparatus as to produce curve Q.

Column 2 gives the arbitrary values in percent for the distortionarising within the recording apparatus. 1.

Column 3 gives the relative percent of energy recorded on the originalor primary film, and

which are the same as the values of column 2.

Column 4 gives the arbitrary values in percent for the distortionarising within the reproduc- Column 5 gives the resultant relativereproduction in percentage reproduced from the sound record of column 3by the reproducing apparatus column 4. V

The values in this column correspond to curve Q of Fig 10.

Column 6 gives the relative percentage of the reproduction of column 5that is recorded on the secondary record, when using recording apparatushaving characteristics similar to that of column 2. 7

Column 7 gives the relative percentage of the recorded energy that is tobe reproduced on apparatus similar to that of Fig. 6, when the energyrecorded on the primary record of column 3 is partially neutralized bysubtracting 80% of the secondary record of column 6.

Column 8 gives the relative percentage of reproduction obtainable forthe various frequencies,

when the partially neutralized record of column '7 is reproduced onapparatus similar to that of Fig. 6 and having characteristics similarto that of column 4. These values correspond to curve B of Fig. 10.

The comparison of curve Q and curve R of Fig. 10 shows quite clearly theresult obtained by subtracting 80% of the secondary record from thedirect record. This partial neutralization of one record with anotherhas the effect of reducing the volume of the reproduced sound as well astending to correct for distortion. Therefore, additional amplificationwill be required in the reproducing apparatus to overcome this reductionin volume. Curve R2 shows the result obtained by increasing theamplification approximately four fold over that used in obtaining curveR.

If the reduction in volume, caused by distortion of the variousimportant frequencies were such as could be represented by the letters Ato F, and there were no frequencies reproduced as poorly as thoserepresented by the letters G to J, it would be necessary to subtractonly about 70% of the secondary record from the direct record in orderto obtain the most advantageous results. Column 9 and column 10 show theresults-obtained under this condition. Curve S of Fig,'10 whichcorresponds to the values given in column 10, shows clearly that therelative improvement is greater in this case than that of curve B andleads to the conclusion that the less the distortion within theapparatus, still greater will be the improvement effected by the presentinvention.

bining synchronously the products of two input apparatuses in parallelwith each other, one of which input apparatuses is corrective and hasdistorting characteristics over said band of frequencies similar to thedistorting characteristics of the reproducing apparatus, and applyingsaid combined products to said reproducing apparatus.

5. A method of obtaining faithful reproduction of sound fromsound-reproducing apparatus including an amplifier and a loud speaker,both having distorting characteristics over a substantial band offrequencies, which method comprises Direct1 reciirtgi neutra ize y so%of SecOldfg ary recor Sound g g fgygggg Relative oi Relative oi Relativeoi Relative of gfig gg gf gg repro- Freby the direct energy recordenergypassed sound reproenergy recordmt is g duced qucncy recording ed ondirect by the reprodueed for 500- ed on second- 1 for both from acircuit record ducing circuit ondary record my record mmy andneiiggrialondary circuits direct when operatrecord ing at frequency APercent100 Percent 00 Percent Percent Percent 0 Percent Pcrcem2 l 100 10 0 100 100 90 90 90 28 25 90 90 90 81 73 31 28 70 70 100 70 49 31 31 i090 66 (:0 51 i7 31 75 66 50 37 16 i1 100 100 40 i0 40 (v8 27 60 60 50 3018 46 23 8O 25 20 16 67 17 100 l0 l0 10 92 09 I claim:

1. Sound recording means comprising a sound recording circuit for makinga permanent record corresponding to the sound waves energizing saidcircuit, a sound reproducing circuit energized by the output of saidrecording circuit, and a second sound recording circuit havingdistorting characteristics similar to the distorting characteristics ofsaid first recording circuit energized by sound reproduced by saidreproducing circuit for making a second permanent record on the samerecording medium as used for the recording from said first recordingcircuit.

2. A method of obtaining faithful reproduction of sound fromsound-reproducing apparatus having distorting characteristics over asubstantial band of frequencies which method comprises combiningsynchronously the products of two sound input apparatuses in parallelwith each other, one of which input apparatuses is corrective and hasdistorting characteristics over said band of frequencies similar to thedistorting characteristics of the reproducing apparatus, and applyingsaid combined products to said soundreproducing apparatus.

3. A method of obtaining faithful reproduc tion of sound fromsound-reproducing apparatus including a loud speaker having distortingcharacteristics over a substantial band of frequencies, which methodcomprises combining synchronously the products of two sound inputapparatuses in parallel with each other, one of which sound inputapparatuses is corrective and includes a loud speakers having distortingcharacteristics over said band of frequencies similar to those of theloud speaker used in the reproducing apparatus and applying saidcombined products to said sound-reproducing apparatus.

4. A method of obtaining faithful reproduction of sense-affecting wavesfrom reproducing apparatus having distorting characteristics over asubstantial band of frequencies, which method comprises applying saidwaves to said apparatus comcombining synchronously the products of twosound input apparatuses in parallel with each other, one of which inputapparatuses is corrective and includes an amplifier and loud speakerhaving distorting characteristics over said band of frequencies similarto those of the amplifier and loud speaker, respectively, of thereproducing apparatus, and applying said combined prod nets to saidsound-reproducing apparatus.

6. Apparatus for obtaining faithful reproduction of sound fromsound-reproducing apparatus having distorting characteristics over asubstantial band of frequencies, which apparatus comprises two soundinput apparatuses in parallel With each other, one of which inputapparatuses is corrective and has distorting characteristics over saidband of frequencies similar to the distorting characteristics of thereproducing apparatus, and means for combining synchronously theproducts of said two sound input apparatuses.

7. Apparatus for obtaining faithful reproduction of sound fromsound-reproducing apparatus including a loud speaker having distortingcharacteristics over a substantial band of frequencies, which apparatuscomprises two sound input apparatuses in parallel with each other, oneof which sound input apparatuses is corrective and includes a loudspeaker having distorting char acteristics over said band of frequenciessimilar to those of the loud speaker used in the reproducing apparatus,and means for combining synchronously the products of said two soundinput apparatuses.

8. Apparatus for obtaining faithful reproduction of sense-affectingwaves from reproducing apparatus having distorting char-acteristics overa substantial band of frequencies, which apparatus comprises two inputapparatuses in p.ar allel with each other, one of which inputapparatuses is corrective and has distorting characteristics over saidband of frequencies similar to the distorting characteristics of thereproducing apparatus, and means for combining synchrois corrective andincludes an amplifier anda loud speaker having distortingcharacteristics over said band of frequencies similar to those of theamplifier and loud speak-er, respectively, of the reproducing apparatus,and means for combining 3 synchronously the products of said'two soundinput apparatuses.

WESLEY WILSON.

